Cylinder liners for diesel internal combustion engines for heavy or large-sized vehicles generally have outer surfaces which are surrounded by a cooling fluid or coolant liquid which acts so as to dissipate the heat generated. These wet cylinder liners, which are better known as wet sleeves or cylinder liners, are susceptible to a fault mechanism known as erosion by cavitation.
Cavitation is the formation of vapor bubbles in liquid mediums which originate from sudden pressure drops. The movement of the cylinders results in high speeds of vibration outside the wet cylinder liner, such that the cooling fluid, when it is accelerated, has pressure reduction below the minimum pressure point at which vaporization of the fluid occurs. Thus, local vaporization of the cooling fluid occurs, forming vapor bubbles. When the local pressure increases once more, the vapor bubbles formed in the fluid collapse. If the region of collapse of the vapor bubbles is close to the outer surface of the liner, the bubbles can give rise to erosions on the surface, thus promoting loss of material, and even rupture of the wet cylinder liner.
Under the conditions described above, the phenomenon of cavitation can occur at any part close to the outer surface of the wet cylinder liner, however two types of recurrent cavitation are observed. A first type of cavitation occurs in the region of greatest force (thrust side or anti-thrust side) of the wet cylinder liner, where impact of the piston occurs, due to the secondary movement. A second type of cavitation occurs in the fitting clearances between the cylinder liner and the engine block, where there are high rates of flow of the cooling fluid. These high rates of flow reduce the local pressure of the fluid, and are affected by small movements by the cylinder liner.
Attempts by previous technology to prevent or reduce the phenomenon of cavitation and the resulting erosion are found in the prior art, such as, for example, in the Korean document KR20070060326, which describes a cylinder liner of the wet type with increased resistance to wear and cavitation. On its outer surface, the cylinder liner receives a polymer coating layer consisting of a polymer with heat conduction properties. A heat conductor agent is added to the polymer, resulting in a heterogeneous coating, with a polymer matrix and heat conductor agents distributed along the matrix.
British document GB76954 describes a cylinder liner of the wet type which receives on its outer surface a natural or synthetic rubber coating, which can be sprayed, vulcanized or set on the surface.
Both the documents described, as well as other techniques encountered, do not provide efficient solutions for the problem of erosion by cavitation and possible rupture of the cylinder liners of the wet type.
It is therefore necessary to find a solution for cylinder liners of the wet type which can guarantee excellent durability when they are subjected to the occurrence of erosion by cavitation, such that the cylinder liner sustains lesser loss of mass, thus preventing the possible rupture of the liner.